Gyrotron Traveling-wave Tube Amplifier Research Articles

Design and simulation of a W-band gyrotron traveling wave amplifier

The design of a W-band gyrotron traveling wave tube amplifier is presented. The device with a lossy ceramic interaction circuit operates in the fundamental harmonic TE01 circular electric mode. The 70-kV, 6-A electron beam is produced by a double anode magnetron injection gun with an average perpendicular-to-parallel velocity ratio of 1.2 and a parallel velocity spread of less than 3%. The beam-wave interaction is investigated by using a particle-in-cell code. The simulations predict that the amplifier can produce an output peak power of over 100 kW, 28% efficiency, 42 dB gain, and a 3 GHz bandwidth, respectively under the assumption of beam velocity spread 3%.

Design and Experiment of a High Average Power Ku-Band TE01 Mode Gyro-TWT

A high power Ku -band TE01 mode gyrotron traveling wave tube amplifier (gyro-TWT) is designed and experimented in this paper. The emphasis is put on the gyro-TWT with a high average power. In the design process, a low average velocity spread magnetron injection electron gun and a wideband multichannel TE01 mode input coupler are adopted. At the same time, a high average power curved collector is also applied. To suppress the potential gyro-backward wave oscillator interactions, a new type lossy ceramic rings and lossy ceramic pieces hybrid loaded structure is used in the high-frequency interaction circuit of gyro-TWT. In hot test, the developed Ku -band TE01 mode gyro-TWT is driven by a 70-kV 23-A helical electron beam and produce a ~31.5 kW maximum saturated output average power at 16.2 GHz, corresponding to a saturated peak power of ~450 kW (7% duty ratio), a saturated gain of ~40.5 dB, an efficiency of ~28%. The measured 3-dB bandwidth is ~2.1 GHz. The gyro-TWT is found to be zero-drive stable at these operating points.

Stability analysis of a two-stage tapered gyrotron traveling-wave tube amplifier with distributed losses

The two-stage tapered gyrotron traveling-wave tube (gyro-TWT) amplifier has achieved wide bandwidth in the millimeter wave range. However, possible oscillations in each stage limit this amplifier's operating beam current and thus its output power. To further enhance the amplifier's stability, distributed losses are applied to the interaction circuit of the two-stage tapered gyro-TWT. A self-consistent particle-tracing code is used for analyzing the beam-wave interactions. The stability analysis includes the effects of the wall losses and the length of each stage on the possible oscillations. Simulation results reveal that the distributed-loss method effectively stabilizes all the oscillations in the two stages. Under stable operating conditions, the device is predicted to produce a peak power of 60 kW with an efficiency of 29% and a saturated gain of 52 dB in the Ka-band. The 3-dB bandwidth is 5.7 GHz, which is approximately 16% of the center frequency.

High-power, stable Ka/V dual-band gyrotron traveling-wave tube amplifier

A dual-band amplifier can reduce the size, cost, and weight of a transmitter in dual-band radar and communication systems. This study proposes and theoretically investigates a gyrotron traveling-wave tube (gyro-TWT) amplifier capable of dual-band operation. Possible oscillations in the coaxial interaction waveguide are stabilized by the lossy inner cylinder. Under stable operating conditions, the gyro-TWT is predicted to provide a peak power of 375 kW with 71 dB saturated gain and 3.8 GHz bandwidth in the Ka-band and a peak power of 150 kW with 35 dB saturated gain and 1.7 GHz bandwidth in the V-band.

Theoretical and Experimental Investigation of a Ka-band Gyro-TWT with Lossy Interaction Structure

The stability analysis of a Ka-band gyrotron traveling-wave tube amplifier (gyro-TWT) operating in the circular TE01 mode at the fundamental cyclotron harmonic is presented. The small signal linear theory is used to analyze the amplification of operation mode and oscillation of parasitic modes. The optimum dielectric parameters including loss layer thickness and permittivity are given. Propagation loss of operation mode is 3 dB/cm with the thickness of loss layer d = 0.7 mm and relative permittivity ξ″ = 11−6j, and propagation loss per unit length of parasitic modes TE11, TE21, TE02 at each oscillation frequency (24.85 GHz, 27.85 GHz, 61.2 GHz) is 2.5 dB/cm, 6 dB/cm, 7.5 dB/cm, respectively, sufficient to suppress oscillations of operation and parasitic modes. Taking advantage of the optimized parameters of loaded dielectric, a high gain scheme has been demonstrated in a 34-GHz, TE01-mode gyro-TWT, producing 160 kW saturated output power at 40 dB stable gain and 22.8% efficiency with a 3-dB bandwidth of 5%.

Relativistic performance analysis of a high current density magnetron injection gun

Electron beam quality is essential to the performance of millimeter-wave gyroamplifiers, particularly the gyrotron traveling-wave tube amplifier, which is extremely sensitive to the electron velocity spread and emission uniformity. As one moves up in power and frequency, the quality of the electron beam becomes even more critical. One aspect of the electron beam formation technology which has received relatively little attention has been the performance analysis of the electron beam itself. In this study, a 100 kV, 8 A magnetron injection gun with a calculated perpendicular-to-parallel velocity ratio of 1.4 and axial velocity spread of 3.5% has been designed, tested, and analyzed. It is shown that the equipment precision and a fully relativistic data analysis model afford sufficient resolution to allow a verification of the theoretical predictions as well as a quantitative inference to the surface roughness of the cathode used.

Third-Harmonic Frequency Multiplication of a Two-Stage Tapered Gyrotron TWT Amplifier

The frequency multiplication of a two-stage tapered gyrotron traveling wave tube amplifier is experimentally verified in low-voltage and low-current operation. By modulating an axis-encircling electron beam at the fundamental harmonic cyclotron frequency in the input stage, a frequency-tripled signal induced by the third-harmonic component of the modulated beam current is chosen to be extracted from the output stage. Both interaction stages are linearly tapered to improve stability and bandwidth. The third-harmonic frequency multiplication is predicted theoretically and investigated using a self-consistent large-signal theory and a particle-in-cell code simulation, which estimate a pure third-harmonic generation and a power-scaling law. In the experiment, X-band drive signals from 10.6-12 GHz are multiplied by a factor of three to produce Ka-band output frequencies from 31.8-36 GHz, showing reasonable agreement with theoretical predictions for a 30-kV, 160-mA axis-encircling electron beam.

A two-stream gyrotron traveling wave tube amplifier

A new idea of using two electron beams to widen the bandwidth of a Gyrotron Traveling Wave Tube Amplifier is put forward. Theoretical and numerical investigation show that the new model can produce wideband and high power output and its gain is much higher compared to the existing wideband model. When the current of the two beams is 10 A, their voltages are, respectively, 90 and 153 kV, the velocity ratios are 1.0 and 0.62, and their axial momentum spreads are 5.5% and 1.2%, the output saturated bandwidth can reach at least 22%, the peak power, efficiency and gain are 395 kW, 16% and 62 dB, respectively. If the axial guiding magnetic field is tapered near the end of the interaction region, a constant bandwidth of 23% with a peak output power 280 kW can be achieved.

Nonlinear theory of a folded waveguide gyrotron traveling-wave tube amplifier.

We have developed a three-dimensional nonlinear theory for broadband gyrotron traveling-wave amplification in an H-plane-bend folded waveguide. The H-plane-bend configuration is formed by folding a rectangular waveguide so that the orientation of the magnetic field changes along the bend in contrast to the conventional E-plane bend, where the orientation of the electric field changes. Calculations show the feasibility of amplifier operation with large instantaneous bandwidth and moderate efficiency both in the slow wave region and the reduced dispersion fast wave region. Numerical results for a cold beam show an efficiency of 26% with 11% bandwidth in the slow wave region and an efficiency of 47% with 10% bandwidth in the fast wave region. For an electron beam with 2% velocity spread and 2% guiding center spread, the slow wave efficiency drops to 6% but the bandwidth increases to 16% whereas the efficiency and bandwidth of the fast waves decrease by a small amount to 42% and 9.5%, respectively. The efficiency is more sensitive to the axial beam velocity spread in the slow wave region due to larger Doppler shift. (c) 1995 The American Physical Society

Gain Broadening of Two-Stage Tapered Gyrotron Traveling Wave Tube Amplifier

The first operation of a two-stage tapered gyrotron traveling wave amplifier employing two tapered waveguide circuits and tapered magnetic fields is reported. Small-signal gain of 30 dB and saturated gain of 25 dB over a 20% bandwidth at an efficiency of 16% have been observed using a 33 kV, 1.5 A electron beam. Comparison with supporting theory is satisfactory.

Nonlinear dynamics of the gyrotron traveling wave amplifier

Mode interactions in the gyrotron traveling wave tube amplifier (gyro-TWT) are examined with particle simulations and compared with experimental observations. Studies focus on the competition between the absolute and convective instabilities. Detailed diagnostics on mode structures, field growth profiles, and evolution of electron distribution in momentum and energy spaces allow an in depth look at the basic physical processes, such as the mechanism of mode competition and suppression. Mutual verifications between the theory and experiment have strengthened understanding of the multimode behavior and added to the predictability of high-power gyro-TWT’s.